Methods have widely been adopted that use a heated roller in order to fix a toner-visualized electrostatic latent image in electrophotography.
For the use of this method, it is desired that the lowest fixing temperature (Tf: the lowest temperature of a heated roller at which a fixing level of 70% is obtained) of a toner is low, and that the hot offset temperature (Th: the lowest temperature of a heated roller at which the hot offset occurs) is high. To meet these two needs, the molecular weight distribution of a toner binder has been frequently proposed to be made to widely range from low molecular weights to high molecular weights (e.g. U.S. Pat. Nos. 4,386,147 and 4,486,524).
However, attempts to render the molecular weights of the low molecular weight region to make lower and to increase the low molecular weight ratio for the purpose of lowering the lower limit of the fixing temperature poses the problem of the image deterioration being likely to occur during running of the toner.